Budget big-batch gravy

Ingredients

• 2kg chicken wings
• 2 rashers bacon
• 1 head garlic, halved
• 2 brown onions, halved
• 3 carrots, roughly chopped
• 2 sticks celery, roughly chopped
• 2 bay leaves
• 1 tbsp olive oil
• 1 1/2 cups plain flour
• 5 litres boiling water
• 2 tbsp soy sauce
• 2 tbsp Worcestershire sauce
• 2 tbsp tomato sauce
• 2 tsp chicken stock powder
• 1-2 tsp salt